Semiconductor device and method of confining conductive bump material during reflow with solder mask patch

ABSTRACT

A semiconductor device has a semiconductor die with die bump pads and substrate with trace lines having integrated bump pads. A solder mask patch is formed interstitially between the die bump pads or integrated bump pads. The solder mask patch contains non-wettable material. Conductive bump material is deposited over the integrated bump pads or die bump pads. The semiconductor die is mounted over the substrate so that the conductive bump material is disposed between the die bump pads and integrated bump pads. The bump material is reflowed without a solder mask around the integrated bump pads to form an interconnect between the semiconductor die and substrate. The solder mask patch confines the conductive bump material within a footprint of the die bump pads or integrated bump pads during reflow. The interconnect can have a non-fusible base and fusible cap.

CLAIM TO DOMESTIC PRIORITY

The present non-provisional application claims the benefit of priorityof U.S. Provisional Application Ser. No. 61/141,782, filed Dec. 31,2008.

FIELD OF THE INVENTION

The present invention relates in general to semiconductor devices and,more particularly, to a semiconductor device and method of confiningconductive bump material during reflow with solder mask patch.

BACKGROUND OF THE INVENTION

Semiconductor devices are commonly found in modern electronic products.Semiconductor devices vary in the number and density of electricalcomponents. Discrete semiconductor devices generally contain one type ofelectrical component, e.g., light emitting diode (LED), small signaltransistor, resistor, capacitor, inductor, and power metal oxidesemiconductor field effect transistor (MOSFET). Integrated semiconductordevices typically contain hundreds to millions of electrical components.Examples of integrated semiconductor devices include microcontrollers,microprocessors, charged-coupled devices (CCDs), solar cells, anddigital micro-mirror devices (DMDs).

Semiconductor devices perform a wide range of functions such ashigh-speed calculations, transmitting and receiving electromagneticsignals, controlling electronic devices, transforming sunlight toelectricity, and creating visual projections for television displays.Semiconductor devices are found in the fields of entertainment,communications, power conversion, networks, computers, and consumerproducts. Semiconductor devices are also found in military applications,aviation, automotive, industrial controllers, and office equipment.

Semiconductor devices exploit the electrical properties of semiconductormaterials. The atomic structure of semiconductor material allows itselectrical conductivity to be manipulated by the application of anelectric field or base current or through the process of doping. Dopingintroduces impurities into the semiconductor material to manipulate andcontrol the conductivity of the semiconductor device.

A semiconductor device contains active and passive electricalstructures. Active structures, including bipolar and field effecttransistors, control the flow of electrical current. By varying levelsof doping and application of an electric field or base current, thetransistor either promotes or restricts the flow of electrical current.Passive structures, including resistors, capacitors, and inductors,create a relationship between voltage and current necessary to perform avariety of electrical functions. The passive and active structures areelectrically connected to form circuits, which enable the semiconductordevice to perform high-speed calculations and other useful functions.

Semiconductor devices are generally manufactured using two complexmanufacturing processes, i.e., front-end manufacturing, and back-endmanufacturing, each involving potentially hundreds of steps. Front-endmanufacturing involves the formation of a plurality of die on thesurface of a semiconductor wafer. Each die is typically identical andcontains circuits formed by electrically connecting active and passivecomponents. Back-end manufacturing involves singulating individual diefrom the finished wafer and packaging the die to provide structuralsupport and environmental isolation.

One goal of semiconductor manufacturing is to produce smallersemiconductor devices. Smaller devices typically consume less power,have higher performance, and can be produced more efficiently. Inaddition, smaller semiconductor devices have a smaller footprint, whichis desirable for smaller end products. A smaller die size may beachieved by improvements in the front-end process resulting in die withsmaller, higher density active and passive components. Back-endprocesses may result in semiconductor device packages with a smallerfootprint by improvements in electrical interconnection and packagingmaterials.

FIGS. 1 and 2 illustrate a cross-sectional view and top view of aportion of flipchip type semiconductor die 10 and interconnects or bumps12 metallurgically and electrically connected between bump pads 18 asformed on semiconductor die 10 and trace lines 20 and 22 as formed onsubstrate 30. Trace line 22 is routed between traces lines 20 and bumps12 on substrate 30. Trace lines 20 and 22 are electrical signalconductors with optional bump pads for mating to bumps 12-14. Soldermask 26 overlays trace lines 20 and 22. Solder mask or registrationopenings (SRO) 28 are formed over substrate 30 to expose trace lines 20and 22. SRO 28 confines the conductive bump material on the bump pads oftrace lines 20 and 22 during reflow and prevents the molten bumpmaterial from leaching onto the trace lines, which can cause electricalshorts to adjacent structures. SRO 28 is made larger than the trace lineor bump pad. SRO 28 is typically circular in shape and made as small aspossible to reduce the pitch of trace lines 20 and 22 and increaserouting density.

In typical design rules, the minimum escape pitch of trace line 30 isdefined by P=(1.1 D+W)/2+L, where D is bump base diameter, W is traceline width, and L is the ligament separation between SRO and adjacentstructures. Using a solder registration design rule of ±30 micrometers(μm), D of 100 μm, W of 20 μm, and L of 30 μm, the minimum escape pitchof trace lines 30-34 is (1.1*100+20)/2+30=95 μm. SRO 28 around the bumppads limits the escape pitch and routing density of the semiconductordie.

SUMMARY OF THE INVENTION

A need exists to minimize escape pitch of trace lines for higher routingdensity. Accordingly, in one embodiment, the present invention is amethod of making a semiconductor device comprising the steps ofproviding a semiconductor die having die bump pads, providing asubstrate having trace lines with integrated bump pads, forming a soldermask patch interstitially between the die bump pads or integrated bumppads, depositing conductive bump material on the integrated bump pads ordie bump pads, mounting the semiconductor die over the substrate so thatthe conductive bump material is disposed between the die bump pads andintegrated bump pads, and reflowing the conductive bump material withouta solder mask around the integrated bump pads to form an interconnectbetween the semiconductor die and substrate. The solder mask patchconfines the conductive bump material within a footprint of the die bumppads or integrated bump pads during reflow.

In another embodiment, the present invention is a method of making asemiconductor device comprising the steps of providing a firstsemiconductor structure having first bump pads, providing a secondsemiconductor structure having second bump pads, forming a solder maskpatch between the first bump pads or second bump pads, depositingconductive bump material between the first and second bump pads,mounting the first semiconductor structure over the second semiconductorstructure so that the conductive bump material is disposed between thefirst bump pads and second bump pads, and reflowing the conductive bumpmaterial without a solder mask around the first and second bump pads toform an interconnect. The solder mask patch confines the conductive bumpmaterial within a footprint of the first bump pads or second bump padsduring reflow.

In another embodiment, the present invention is a method of making asemiconductor device comprising the steps of providing a substratehaving trace lines with integrated bump pads, forming a solder maskpatch between the integrated bump pads, depositing conductive bumpmaterial on the integrated bump pads, and reflowing the conductive bumpmaterial without a solder mask around the integrated bump pads to forman interconnect. The solder mask patch confines the conductive bumpmaterial within a footprint of the integrated bump pads during reflow.

In another embodiment, the present invention is a semiconductor devicecomprising a semiconductor die having first bump pads and substratehaving second bump pads. A solder mask patch is formed between the firstbump pads or second bump pads. An interconnect is formed between thefirst and second bump pads by reflowing conductive bump material withouta solder mask around the second bump pads. The solder mask patchconfines the conductive bump material within the first bump pads andsecond bump pads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of conventional interconnectsformed between a semiconductor die and trace lines on a substrate;

FIG. 2 illustrates a top view of conventional interconnects formed overthe trace lines through solder mask openings;

FIG. 3 illustrates a PCB with different types of packages mounted to itssurface;

FIGS. 4 a-4 d illustrate further detail of the representativesemiconductor packages mounted to the PCB;

FIG. 5 illustrates interconnects formed between a semiconductor die andtrace lines on a substrate;

FIGS. 6 a-6 c illustrate integrated bump pads along the trace lines;

FIG. 7 illustrates a solder mask patch formed interstitially within thearray of integrated bump pads on the substrate;

FIG. 8 illustrates bumps formed on the integrated bump pads with bumpmaterial confined by the solder mask patch during reflow;

FIGS. 9 a-9 b illustrate a composite interconnect with non-fusible baseand fusible cap; and

FIGS. 10 a-10 d illustrate a tapered composite interconnect withnon-fusible base and fusible cap.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in one or more embodiments in thefollowing description with reference to the figures, in which likenumerals represent the same or similar elements. While the invention isdescribed in terms of the best mode for achieving the invention'sobjectives, it will be appreciated by those skilled in the art that itis intended to cover alternatives, modifications, and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims and their equivalents as supported by the followingdisclosure and drawings.

Semiconductor devices are generally manufactured using two complexmanufacturing processes: front-end manufacturing and back-endmanufacturing. Front-end manufacturing involves the formation of aplurality of die on the surface of a semiconductor wafer. Each die onthe wafer contains active and passive electrical components, which areelectrically connected to form functional electrical circuits. Activeelectrical components, such as transistors and diodes, have the abilityto control the flow of electrical current. Passive electricalcomponents, such as capacitors, inductors, resistors, and transformers,create a relationship between voltage and current necessary to performelectrical circuit functions.

Passive and active components are formed over the surface of thesemiconductor wafer by a series of process steps including doping,deposition, photolithography, etching, and planarization. Dopingintroduces impurities into the semiconductor material by techniques suchas ion implantation or thermal diffusion. The doping process modifiesthe electrical conductivity of semiconductor material in active devices,transforming the semiconductor material into an insulator, conductor, ordynamically changing the semiconductor material conductivity in responseto an electric field or base current. Transistors contain regions ofvarying types and degrees of doping arranged as necessary to enable thetransistor to promote or restrict the flow of electrical current uponthe application of the electric field or base current.

Active and passive components are formed by layers of materials withdifferent electrical properties. The layers can be formed by a varietyof deposition techniques determined in part by the type of materialbeing deposited. For example, thin film deposition may involve chemicalvapor deposition (CVD), physical vapor deposition (PVD), electrolyticplating, and electroless plating processes. Each layer is generallypatterned to form portions of active components, passive components, orelectrical connections between components.

The layers can be patterned using photolithography, which involves thedeposition of light sensitive material, e.g., photoresist, over thelayer to be patterned. A pattern is transferred from a photomask to thephotoresist using light. The portion of the photoresist patternsubjected to light is removed using a solvent, exposing portions of theunderlying layer to be patterned. The remainder of the photoresist isremoved, leaving behind a patterned layer. Alternatively, some types ofmaterials are patterned by directly depositing the material into theareas or voids formed by a previous deposition/etch process usingtechniques such as electroless and electrolytic plating.

Depositing a thin film of material over an existing pattern canexaggerate the underlying pattern and create a non-uniformly flatsurface. A uniformly flat surface is required to produce smaller andmore densely packed active and passive components. Planarization can beused to remove material from the surface of the wafer and produce auniformly flat surface. Planarization involves polishing the surface ofthe wafer with a polishing pad. An abrasive material and corrosivechemical are added to the surface of the wafer during polishing. Thecombined mechanical action of the abrasive and corrosive action of thechemical removes any irregular topography, resulting in a uniformly flatsurface.

Back-end manufacturing refers to cutting or singulating the finishedwafer into the individual die and then packaging the die for structuralsupport and environmental isolation. To singulate the die, the wafer isscored and broken along non-functional regions of the wafer called sawstreets or scribes. The wafer is singulated using a laser cutting toolor saw blade. After singulation, the individual die are mounted to apackage substrate that includes pins or contact pads for interconnectionwith other system components. Contact pads formed over the semiconductordie are then connected to contact pads within the package. Theelectrical connections can be made with solder bumps, stud bumps,conductive paste, or wirebonds. An encapsulant or other molding materialis deposited over the package to provide physical support and electricalisolation. The finished package is then inserted into an electricalsystem and the functionality of the semiconductor device is madeavailable to the other system components.

FIG. 3 illustrates electronic device 50 having a chip carrier substrateor printed circuit board (PCB) 52 with a plurality of semiconductorpackages mounted on its surface. Electronic device 50 may have one typeof semiconductor package, or multiple types of semiconductor packages,depending on the application. The different types of semiconductorpackages are shown in FIG. 3 for purposes of illustration.

Electronic device 50 may be a stand-alone system that uses thesemiconductor packages to perform one or more electrical functions.Alternatively, electronic device 50 may be a subcomponent of a largersystem. For example, electronic device 50 may be a graphics card,network interface card, or other signal processing card that can beinserted into a computer. The semiconductor package can includemicroprocessors, memories, application specific integrated circuits(ASIC), logic circuits, analog circuits, RF circuits, discrete devices,or other semiconductor die or electrical components.

In FIG. 3, PCB 52 provides a general substrate for structural supportand electrical interconnect of the semiconductor packages mounted on thePCB. Conductive signal traces 54 are formed over a surface or withinlayers of PCB 52 using evaporation, electrolytic plating, electrolessplating, screen printing, or other suitable metal deposition process.Signal traces 54 provide for electrical communication between each ofthe semiconductor packages, mounted components, and other externalsystem components. Traces 54 also provide power and ground connectionsto each of the semiconductor packages.

In some embodiments, a semiconductor device has two packaging levels.First level packaging is a technique for mechanically and electricallyattaching the semiconductor die to an intermediate carrier. Second levelpackaging involves mechanically and electrically attaching theintermediate carrier to the PCB. In other embodiments, a semiconductordevice may only have the first level packaging where the die ismechanically and electrically mounted directly to the PCB.

For the purpose of illustration, several types of first level packaging,including wire bond package 56 and flip chip 58, are shown on PCB 52.Additionally, several types of second level packaging, including ballgrid array (BGA) 60, bump chip carrier (BCC) 62, dual in-line package(DIP) 64, land grid array (LGA) 66, multi-chip module (MCM) 68, quadflat non-leaded package (QFN) 70, and quad flat package 72, are shownmounted on PCB 52. Depending upon the system requirements, anycombination of semiconductor packages, configured with any combinationof first and second level packaging styles, as well as other electroniccomponents, can be connected to PCB 52. In some embodiments, electronicdevice 50 includes a single attached semiconductor package, while otherembodiments call for multiple interconnected packages. By combining oneor more semiconductor packages over a single substrate, manufacturerscan incorporate pre-made components into electronic devices and systems.Because the semiconductor packages include sophisticated functionality,electronic devices can be manufactured using cheaper components and astreamlined manufacturing process. The resulting devices are less likelyto fail and less expensive to manufacture resulting in a lower cost forconsumers.

FIGS. 4 a-4 d show exemplary semiconductor packages. FIG. 4 aillustrates further detail of DIP 64 mounted on PCB 52. Semiconductordie 74 includes an active region containing analog or digital circuitsimplemented as active devices, passive devices, conductive layers, anddielectric layers formed within the die and are electricallyinterconnected according to the electrical design of the die. Forexample, the circuit may include one or more transistors, diodes,inductors, capacitors, resistors, and other circuit elements formedwithin the active region of semiconductor die 74. Contact pads 76 areone or more layers of conductive material, such as aluminum (Al), copper(Cu), tin (Sn), nickel (Ni), gold (Au), or silver (Ag), and areelectrically connected to the circuit elements formed withinsemiconductor die 74. During assembly of DIP 64, semiconductor die 74 ismounted to an intermediate carrier 78 using a gold-silicon eutecticlayer or adhesive material such as thermal epoxy. The package bodyincludes an insulative packaging material such as polymer or ceramic.Conductor leads 80 and wire bonds 82 provide electrical interconnectbetween semiconductor die 74 and PCB 52. Encapsulant 84 is depositedover the package for environmental protection by preventing moisture andparticles from entering the package and contaminating die 74 or wirebonds 82.

FIG. 4 b illustrates further detail of BCC 62 mounted on PCB 52.Semiconductor die 88 is mounted over carrier 90 using an underfill orepoxy-resin adhesive material 92. Wire bonds 94 provide first levelpacking interconnect between contact pads 96 and 98. Molding compound orencapsulant 100 is deposited over semiconductor die 88 and wire bonds 94to provide physical support and electrical isolation for the device.Contact pads 102 are formed over a surface of PCB 52 using a suitablemetal deposition such as electrolytic plating or electroless plating toprevent oxidation. Contact pads 102 are electrically connected to one ormore conductive signal traces 54 in PCB 52. Bumps 104 are formed betweencontact pads 98 of BCC 62 and contact pads 102 of PCB 52.

In FIG. 4 c, semiconductor die 58 is mounted face down to intermediatecarrier 106 with a flip chip style first level packaging. Active region108 of semiconductor die 58 contains analog or digital circuitsimplemented as active devices, passive devices, conductive layers, anddielectric layers formed according to the electrical design of the die.For example, the circuit may include one or more transistors, diodes,inductors, capacitors, resistors, and other circuit elements withinactive region 108. Semiconductor die 58 is electrically and mechanicallyconnected to carrier 106 through bumps 110.

BGA 60 is electrically and mechanically connected to PCB 52 with a BGAstyle second level packaging using bumps 112. Semiconductor die 58 iselectrically connected to conductive signal traces 54 in PCB 52 throughbumps 110, signal lines 114, and bumps 112. A molding compound orencapsulant 116 is deposited over semiconductor die 58 and carrier 106to provide physical support and electrical isolation for the device. Theflip chip semiconductor device provides a short electrical conductionpath from the active devices on semiconductor die 58 to conductiontracks on PCB 52 in order to reduce signal propagation distance, lowercapacitance, and improve overall circuit performance. In anotherembodiment, the semiconductor die 58 can be mechanically andelectrically connected directly to PCB 52 using flip chip style firstlevel packaging without intermediate carrier 106.

In another embodiment, active area 108 of semiconductor die 58 isdirectly mounted facedown to PCB 115, i.e., without an intermediatecarrier, as shown in FIG. 4 d. Bump pads 111 are formed on active area108 using an evaporation, electrolytic plating, electroless plating,screen printing, or other suitable metal deposition process. Bump pads111 connect to the active and passive circuits by conduction tracks inactive area 108. Bump pads 111 can be Al, Sn, Ni, Au, Ag, or Cu. Anelectrically conductive bump material is deposited over bump pads 111 orconduction tracks 118 in PCB 115 using an evaporation, electrolyticplating, electroless plating, ball drop, or screen printing process. Thebump material can be Al, Sn, Ni, Au, Ag, lead (Pb), Bi, Cu, solder, andcombinations thereof, with an optional flux material. For example, thebump material can be eutectic Sn/Pb, high-lead solder, or lead-freesolder. The bump material is bonded between die bump pads 111 andconduction tracks 118 on PCB 115 using a suitable attachment or bondingprocess. In one embodiment, the bump material is reflowed by heating thematerial above its melting point to form spherical balls or bumps 117.The flip chip semiconductor device provides a short electricalconduction path from the active devices on semiconductor die 58 toconduction tracks 118 on PCB 115 in order to reduce signal propagation,lower capacitance, and achieve overall better circuit performance.

FIG. 5 illustrates a cross-sectional view of a portion of flipchip typesemiconductor die 120 with bump pads 122. Trace lines 130 and 132 areformed on substrate 136. Trace lines 130 and 132 are straight electricalconductors with integrated bump pads 138, as shown in FIG. 6 a. Theintegrated bump pads 138 are co-linear with trace lines 130 and 132.Alternatively, trace lines 130 and 132 can have round integrated bumppads 139, as shown in FIG. 6 b, or rectangular integrated bump pads 140,as shown in FIG. 6 c. The integrated bump pads are typically arranged inan array for maximum interconnect density and capacity.

In FIG. 7, solder mask 142 is deposited over a portion of trace lines130 and 132. However, solder mask 142 is not formed over integrated bumppads 138. Consequently, there is no SRO for each bump pad on thesubstrate, as found in prior art FIG. 2. A non-wettable solder maskpatch 144 is formed on substrate 136 interstitially within the array ofintegrated bump pads 138, i.e., between adjacent bump pads. The soldermask patch can also be formed on semiconductor die 10 interstitiallywithin the array of die bump pads 122. More generally, the solder maskpatch is formed in close proximity to the integrated bump pads in anyarrangement to prevent run-out to less wettable areas. FIG. 8 showsbumps 150 and 152 formed over integrated bump pads 138 and confined bysolder mask patch 144.

An electrically conductive bump material is deposited over die bump pads122 or integrated bump pads 138 using an evaporation, electrolyticplating, electroless plating, ball drop, or screen printing process. Thebump material can be Al, Sn, Ni, Au, Ag, Pb, Bi, Cu, solder, andcombinations thereof, with an optional flux solution. For example, thebump material can be eutectic Sn/Pb, high-lead solder, or lead-freesolder. The bump material is bonded to integrated bump pads 138 using asuitable attachment or bonding process. In one embodiment, the bumpmaterial is reflowed by heating the material above its melting point toform spherical balls or bumps 150, 152, and 152. In some applications,bumps 150 and 152 are reflowed a second time to improve electricalcontact to die bump pads 122 and integrated bump pads 138. The bumps canalso be compression bonded to die bump pads 122 and integrated bump pads138. Bumps 150 and 152 represent one type of interconnect structure thatcan be formed over integrated bump pads 138. The interconnect structurecan also use stud bump, micro bump, or other electrical interconnect.

In high routing density applications, it is desirable to minimize escapepitch. In order to reduce the pitch between trace lines 130 and 132, thebump material is reflowed without a solder mask around integrated bumppads 138. The escape pitch between trace lines 130 and 132 can bereduced by eliminating the solder mask and associated SROs around theintegrated bump pads for solder reflow containment, i.e., by reflowingthe bump material without a solder mask. Solder mask 142 may be formedover a portion of traces lines 130 and 132 and substrate 136 away fromintegrated bump pads 138, as shown in FIG. 7. However, solder mask 142is not formed over integrated bump pads 138. That is, the portion oftrace lines 130 and 132 designed to mate with the bump material isdevoid of an SRO formed in solder mask 142.

In addition, solder mask patch 144 is formed on substrate 136interstitially within the array of integrated bump pads 138. Solder maskpatch 144 is non-wettable material. Solder mask patch 144 can be thesame material as solder mask 142 and applied during the same processingstep, or a different material during a different processing step. Soldermask patch 144 can be formed by selective oxidation, plating, or othertreatment of the portion of the trace or pad within the array ofintegrated bump pads 138. Solder mask patch 144 confines solder flow tointegrated bump pads 138 and prevents leaching of conductive bumpmaterial to adjacent structures.

When the bump material is reflowed with solder mask patch 144interstitially disposed within the array of integrated bump pads 138,the wetting and surface tension causes the bump material to be confinedand retained within the space between die bump pads 122 and integratedbump pads 138 and portion of substrate 136 immediately adjacent to tracelines 130 and 132 and substantially within the footprint of theintegrated bump pads 138.

To achieve the desired confinement property, the bump material can beimmersed in a flux solution prior to placement on die bump pad 122 orintegrated bump pads 138 to selectively render the region contacted bythe bump material more wettable than the surrounding area of trace lines130 and 132. The molten bump material remains confined substantiallywithin the area defined by the bump pads due to the wettable propertiesof the flux solution. The bump material does not run-out to the lesswettable areas. A thin oxide layer or other insulating layer can beformed over areas where bump material is not intended to make the arealess wettable. Hence, solder mask 142 is not needed around die bump pads122 or integrated bump pads 138.

Since no SRO is formed around die bump pads 122 or integrated bump pads138, trace lines 130 and 132 can be formed with a finer pitch, i.e.,trace lines 130 and 132 can be disposed closer to adjacent structureswithout making contact and forming electrical shorts. Assuming the samesolder registration design rule, the pitch between trace lines 130 and132 is given as P=(1.1 D+W)/2, where D is the base diameter of bump150-152 and W is the width of the trace lines 130 and 132. In oneembodiment, given a bump diameter of 100 μm and trace line width of 20μm, the minimum escape pitch of trace lines 130 and 132 is 65 μm. Thebump formation eliminates the need to account for the ligament spacingof solder mask material between adjacent openings and minimum resolvableSRO, as found in the prior art.

In another embodiment, a composite interconnect is formed between diebump pads and integrated bump pads to achieve the desired confinement ofthe bump material. In FIGS. 9 a-9 b, composite bump 160 has anon-fusible portion 162 and fusible portion 164. The non-fusible portion162 makes up a larger part of composite bump 160 than the fusibleportion 164. The non-fusible portion 162 is fixed to contact pad orinterconnect site 166 of semiconductor die 168. The fusible portion 164is positioned over lead or trace 170 on substrate 172 in FIG. 9 a andbrought into physical contact with lead 170 for reflow. The fusibleportion 164 collapses around lead 170 upon reflow with heat orapplication of pressure, as shown in FIG. 9 b. The non-fusible portion162 does not melt or deform during reflow and retains its form andshape. The non-fusible portion 162 can be dimensioned to provide astandoff distance between semiconductor die 168 and substrate 172. Afinish such as Cu organic solderability preservative (OSP) can beapplied to substrate 172. A mold underfill material 174 is depositedbetween semiconductor die 168 and substrate 172 to fill the gap betweenthe die and substrate.

The non-fusible portion 162 and fusible portion 164 of composite bump160 are made of different bump material. The non-fusible portion 162 canbe Au, Cu, Ni, high-lead solder, or lead-tin alloy. The fusible portion164 can be Sn, lead-free alloy, Sn—Ag alloy, Sn—Ag—Cu alloy,Sn—Ag-indium (In) alloy, eutectic solder, or other tin alloys with Ag,Cu, or Pb.

The height or volume of fusible bump material in relation to thenon-fusible base material is selected to ensure confinement by virtue ofsurface tension forces. During reflow, the fusible base material isconfined around the non-fusible base material due to the solder maskpatch. The fusible bump material around the non-fusible base alsomaintains die placement during reflow. In general the height of thecomposite interconnect is the same or less than the diameter of thebump. In some cases, the height of the composite interconnect is greaterthan the diameter of the interconnect. In one embodiment, given a bumpbase diameter of 100 μm, the non-fusible base is about 45 μm in heightand the fusible cap is about 35 μm in height. The molten bump materialremains confined substantially within the area defined by the bump padsdue to the solder mask patch and because the volume of bump materialdeposited to form the composite bump, including non-fusible base andfusible cap, is selected so that the resulting surface tension issufficient to retain the bump material substantially within thefootprint of the bump pads and prevent run-out to unintended adjacent ornearby areas. Hence, the solder mask patch formed interstitially withthe array of bump pads reduces trace line pitch and increases routingdensity.

During the reflow process, a large number (e.g., thousands) of compositebumps 160 on semiconductor die 168 are attached to interconnect sites ontrace 170 of substrate 172. Some of the bumps 160 may fail to properlyconnect to substrate 172, particularly if die 168 is warped. Recall thatcomposite bump 160 is larger than trace 170. With a proper forceapplied, the fusible portion 164 deforms or extrudes around trace 170and mechanically locks composite bump 160 to substrate 172. Themechanical interlock is formed by nature of the fusible portion 164being softer than trace 170. The mechanical interlock between compositebump 160 and substrate 172 holds the bump to the substrate duringreflow, i.e., the bump and substrate do not lose contact. Accordingly,composite bump 160 mating to substrate 172 reduces the bump connectfailures.

In another embodiment, the composite interconnect formed between diebump pads and integrated bump pads is tapered. Composite bump 180 has anon-fusible portion 182 and fusible portion 184, as shown in FIGS. 10a-10 d. The non-fusible portion 182 makes up a larger part of compositebump 180 than the fusible portion 184. The non-fusible portion 182 isfixed to contact pad or interconnect site 186 of semiconductor die 188.The fusible portion 184 is positioned over lead or trace 190 onsubstrate 192 and brought into physical contact with lead 190 forreflow. Composite bump 180 is tapered along trace 190, i.e., thecomposite bump has a wedge shape, longer along a length of trace 190 andnarrower across trace 190. The tapered aspect of composite bump 180occurs along the length of trace 190. The view in FIG. 10 a shows thenarrowing taper co-linear with trace 190. The view in FIG. 10 b, normalto FIG. 10 a, shows the longer aspect of the wedge-shaped composite bump180. The fusible portion 184 collapses around lead 190 upon reflow withheat or application of pressure as shown in FIGS. 10 c and 10 d. Thenon-fusible portion 182 does not melt or deform during reflow andretains its form and shape. The non-fusible portion 182 can bedimensioned to provide a standoff distance between semiconductor die 188and substrate 192. A finish such as Cu OSP can be applied to substrate192. A mold underfill material 194 is deposited between semiconductordie 188 and substrate 192 to fill the gap between the die and substrate.

The non-fusible portion 182 and fusible portion 184 of composite bump180 are made of different bump material. The non-fusible portion 182 canbe Au, Cu, Ni, high-lead solder, or lead-tin alloy. The fusible portion184 can be Sn, lead-free alloy, Sn—Ag alloy, Sn—Ag—Cu alloy,Sn—Ag-indium (In) alloy, eutectic solder, or other tin alloys with Ag,Cu, or Pb.

During a reflow process, a large number (e.g., thousands) of compositebumps 180 on semiconductor die 188 are attached to interconnect sites ontrace 190 of substrate 192. Some of the bumps 180 may fail to properlyconnect to substrate 192, particularly if die 188 is warped. Recall thatcomposite bump 180 is larger than trace 190. With a proper forceapplied, the fusible portion 184 deforms or extrudes around trace 190and mechanically locks composite bump 180 to substrate 192. Themechanical interlock is formed by nature of the fusible portion 184being softer than trace 190. The mechanical interlock between compositebump 180 and substrate 192 holds the bump to the substrate duringreflow, i.e., the bump and substrate do not lose contact. Accordingly,composite bump 180 mating to substrate 192 reduces the bump connectfailures.

Any stress induced by the interconnect between the die and substrate canresult in damage or failure of the die. The die contains low dielectricconstant (k) materials, which are susceptible to damage from thermallyinduced stress. The tapered composite bump 180 reduces interconnectstress on semiconductor die 188, which results in less damage to the lowk materials and a lower failure rate of the die.

While one or more embodiments of the present invention have beenillustrated in detail, the skilled artisan will appreciate thatmodifications and adaptations to those embodiments may be made withoutdeparting from the scope of the present invention as set forth in thefollowing claims.

1. A method of making a semiconductor device, comprising: providing asemiconductor die having an array of die bump pads; providing asubstrate having a plurality of trace lines with integrated bump padsforming an array of integrated bump pads over the substrate; forming aplurality of isolated mask patches interstitially within the array ofdie bump pads or the array of integrated bump pads; depositing aconductive bump material on the integrated bump pads or die bump pads;mounting the semiconductor die over the substrate so that the conductivebump material is disposed between the die bump pads and integrated bumppads; and reflowing the conductive bump material without a mask aroundthe integrated bump pads to form an interconnect between thesemiconductor die and substrate, wherein the isolated mask patchesconfine the conductive bump material around the die bump pads orintegrated bump pads during reflow.
 2. The method of claim 1, whereinthe isolated mask patches include non-wettable material.
 3. The methodof claim 1, further including immersing the conductive bump material ina flux solution to increase wettability.
 4. The method of claim 1,wherein the interconnect includes a non-fusible base and fusible cap. 5.The method of claim 1, wherein a volume of conductive bump materialdeposited between the die bump pads and integrated bump pads is selectedso that a surface tension maintains confinement of the conductive bumpmaterial around the die bump pads and integrated bump pads duringreflow.
 6. The method of claim 1, wherein a height of the interconnectis equal to or less than a diameter of the interconnect.
 7. The methodof claim 1, wherein an escape pitch of the trace line is given by(1.1D+W)/2, wherein D is a diameter of the interconnect and W is thewidth of the trace line.
 8. A method of making a semiconductor device,comprising: providing a first semiconductor structure having a pluralityof first bump pads; providing a second semiconductor structure having aplurality of second bump pads; forming a mask patch between the firstbump pads or second bump pads; depositing a conductive bump materialbetween the first and second bump pads; mounting the first semiconductorstructure over the second semiconductor structure so that the conductivebump material is disposed between the first bump pads and second bumppads; and reflowing the conductive bump material without a mask aroundthe first and second bump pads to form an interconnect, wherein the maskpatch confines the conductive bump material around the first bump padsor second bump pads during reflow.
 9. The method of claim 8, wherein themask patch includes non-wettable material.
 10. The method of claim 8,further including immersing the conductive bump material in a fluxsolution to increase wettability.
 11. The method of claim 8, wherein theinterconnect includes a non-fusible base and fusible cap.
 12. The methodof claim 8, wherein the volume of conductive bump material depositedbetween the first and second bump pads is selected so that a surfacetension maintains confinement of the conductive bump material around thefirst and second bump pads during reflow.
 13. The method of claim 8,wherein a height of the interconnect is equal to or less than a diameterof the interconnect.
 14. A method of making a semiconductor device,comprising: providing a substrate having trace lines with integratedbump pads; forming a plurality of mask patches between the integratedbump pads; depositing a conductive bump material on the integrated bumppads; and reflowing the conductive bump material without a mask aroundthe integrated bump pads to form an interconnect, wherein the maskpatches confine the conductive bump material around the integrated bumppads during reflow.
 15. The method of claim 14, wherein the mask patchesinclude non-wettable material.
 16. The method of claim 14, furtherincluding immersing the conductive bump material in a flux solution toincrease wettability.
 17. The method of claim 14, wherein theinterconnect includes a non-fusible base and fusible cap.
 18. The methodof claim 14, wherein a volume of conductive bump material deposited overthe integrated bump pads is selected so that a surface tension maintainsconfinement of the conductive bump material around the integrated bumppads during reflow.
 19. The method of claim 14, wherein a height of theinterconnect is equal to or less than a diameter of the interconnect.20. The method of claim 1, wherein a height of the interconnect isgreater than a diameter of the interconnect.
 21. The method of claim 8,wherein a height of the interconnect is greater than a diameter of theinterconnect.
 22. The method of claim 14, wherein a height of theinterconnect is greater than a diameter of the interconnect.
 23. Amethod of making a semiconductor device, comprising: providing asubstrate having a plurality of trace lines with integrated bump pads;forming a mask patch between the integrated bump pads; depositing aconductive bump material on the integrated bump pads; and reflowing theconductive bump material over the integrated bump pads to form aninterconnect.
 24. The method of claim 23, wherein the mask patchconfines the conductive bump material around the integrated bump padsduring reflow.
 25. The method of claim 23, wherein the mask patchesinclude non-wettable material.
 26. The method of claim 23, furtherincluding immersing the conductive bump material in a flux solution toincrease wettability.
 27. The method of claim 23, wherein theinterconnect includes a non-fusible base and fusible cap.
 28. The methodof claim 23, wherein a volume of conductive bump material deposited overthe integrated bump pads is selected so that a surface tension maintainsconfinement of the conductive bump material around the integrated bumppads during reflow.
 29. The method of claim 23, wherein a height of theinterconnect is equal to or less than a diameter of the interconnect.30. The method of claim 23, wherein a height of the interconnect isgreater than a diameter of the interconnect.